From bafa561d0c9363c5307b6b1daa498bd3ae36089d Mon Sep 17 00:00:00 2001 From: Andy Hung Date: Wed, 2 Apr 2014 13:52:10 -0700 Subject: Improve resampler filter computation speed Approximate speed improvement is 10-15% for filter computation, which is floating point intensive. This will be important for devices without hw floating point support. Change-Id: I10b4e778c8d632b52218a777504b092c189e437f Signed-off-by: Andy Hung --- services/audioflinger/AudioResamplerFirGen.h | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-) (limited to 'services/audioflinger') diff --git a/services/audioflinger/AudioResamplerFirGen.h b/services/audioflinger/AudioResamplerFirGen.h index fac3001..1f21c60 100644 --- a/services/audioflinger/AudioResamplerFirGen.h +++ b/services/audioflinger/AudioResamplerFirGen.h @@ -365,6 +365,28 @@ static inline double I0(double x) { } } +/* A speed optimized version of the Modified Bessel I0() which incorporates + * the sqrt and numerator multiply and denominator divide into the computation. + * This speeds up filter computation by about 10-15%. + */ +static inline double I0SqrRat(double x2, double num, double den) { + if (x2 < (3.75 * 3.75)) { + return Poly7(I0Term<0>::value, I0Term<1>::value, + I0Term<2>::value, I0Term<3>::value, + I0Term<4>::value, I0Term<5>::value, + I0Term<6>::value, x2) * num / den; // e < 1.6e-7 + } + num *= Poly9(-0.13544938430e9, -0.33153754512e8, + -0.19406631946e7, -0.48058318783e5, + -0.63269783360e3, -0.49520779070e1, + -0.24970910370e-1, -0.74741159550e-4, + -0.18257612460e-6, x2); // e < 10^(-7.13). + double y = x2 - 225.; // reflection around 15 (squared) + den *= Poly4(-0.34598737196e8, 0.23852643181e6, + -0.70699387620e3, 0.10000000000e1, y); + return num / den; +} + /* * calculates the transition bandwidth for a Kaiser filter * @@ -645,6 +667,7 @@ static inline void firKaiserGen(T* coef, int L, int halfNumCoef, const double xstep = (2. * M_PI) * fcr / L; const double xfrac = 1. / N; const double yscale = atten * L / (I0(beta) * M_PI); + const double sqrbeta = sqr(beta); // We use sine generators, which computes sines on regular step intervals. // This speeds up overall computation about 40% from computing the sine directly. @@ -663,7 +686,8 @@ static inline void firKaiserGen(T* coef, int L, int halfNumCoef, double x = static_cast(ix); // sine generator: sg.valueAdvance() returns sin(ix*xstep); - y = I0(beta * sqrt(1.0 - sqr(x * xfrac))) * yscale * sg.valueAdvance() / x; + // y = I0(beta * sqrt(1.0 - sqr(x * xfrac))) * yscale * sg.valueAdvance() / x; + y = I0SqrRat(sqrbeta * (1.0 - sqr(x * xfrac)), yscale * sg.valueAdvance(), x); } else { y = 2. * atten * fcr; // center of filter, sinc(0) = 1. sg.advance(); -- cgit v1.1